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98 lines
3.3 KiB
Swift
98 lines
3.3 KiB
Swift
import Foundation
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// https://gist.github.com/kristopherjohnson/543687c763cd6e524c91
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/// Find first differing character between two strings
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///
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/// :param: s1 First String
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/// :param: s2 Second String
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///
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/// :returns: .DifferenceAtIndex(i) or .NoDifference
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public func firstDifferenceBetweenStrings(_ s1: String, _ s2: String) -> FirstDifferenceResult {
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let len1 = s1.count
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let len2 = s2.count
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let lenMin = min(len1, len2)
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for i in 0..<lenMin {
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if (s1 as NSString).character(at: i) != (s2 as NSString).character(at: i) {
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return .DifferenceAtIndex(i)
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}
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}
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if len1 < len2 {
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return .DifferenceAtIndex(len1)
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}
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if len2 < len1 {
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return .DifferenceAtIndex(len2)
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}
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return .NoDifference
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}
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/// Create a formatted String representation of difference between strings
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///
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/// :param: s1 First string
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/// :param: s2 Second string
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///
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/// :returns: a string, possibly containing significant whitespace and newlines
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public func prettyFirstDifferenceBetweenStrings(_ s1: String, _ s2: String, previewPrefixLength: Int = 25, previewSuffixLength: Int = 25) -> String {
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let firstDifferenceResult = firstDifferenceBetweenStrings(s1, s2)
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func diffString(at index: Int, _ s1: String, _ s2: String) -> String {
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let markerArrow = "\u{2b06}" // "⬆"
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let ellipsis = "\u{2026}" // "…"
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/// Given a string and a range, return a string representing that substring.
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///
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/// If the range starts at a position other than 0, an ellipsis
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/// will be included at the beginning.
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///
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/// If the range ends before the actual end of the string,
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/// an ellipsis is added at the end.
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func windowSubstring(_ s: String, _ range: NSRange) -> String {
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let validRange = NSMakeRange(range.location, min(range.length, s.count - range.location))
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let substring = (s as NSString).substring(with: validRange)
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let prefix = range.location > 0 ? ellipsis : ""
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let suffix = (s.count - range.location > range.length) ? ellipsis : ""
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return "\(prefix)\(substring)\(suffix)"
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}
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// Show this many characters before and after the first difference
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let windowLength = previewPrefixLength + 1 + previewSuffixLength
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let windowIndex = max(index - previewPrefixLength, 0)
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let windowRange = NSMakeRange(windowIndex, windowLength)
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let sub1 = windowSubstring(s1, windowRange)
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let sub2 = windowSubstring(s2, windowRange)
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let markerPosition = min(previewSuffixLength, index) + (windowIndex > 0 ? 1 : 0)
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let markerPrefix = String(repeating: " ", count: markerPosition)
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let markerLine = "\(markerPrefix)\(markerArrow)"
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return "Difference at index \(index):\n\(sub1)\n\(sub2)\n\(markerLine)"
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}
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switch firstDifferenceResult {
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case .NoDifference: return "No difference"
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case let .DifferenceAtIndex(index): return diffString(at: index, s1, s2)
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}
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}
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/// Result type for firstDifferenceBetweenStrings()
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public enum FirstDifferenceResult {
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/// Strings are identical
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case NoDifference
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/// Strings differ at the specified index.
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///
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/// This could mean that characters at the specified index are different,
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/// or that one string is longer than the other
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case DifferenceAtIndex(Int)
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}
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